







































































DEPARTMENT OF COMMERCE 


Circular 

OP THE 

Bureau of Standards 

S. W. STRATTON, Director 


No. 16 


THE TESTING OF HYDROMETERS 


[4th. Edition] 


Issued February 23,1916 



WASHINGTON 

GOVERNMENT PRINTING OFFICE 
1916 









CIRCULARS 

No. 

2. Measurements of Length and Area, Including Thermal Expansion. 

3. Verification of Standards of Mass. * 

4. Verification of Standards of Capacity. 

5. Testing of Clinical Thermometers. 

6. Fees for Electric, Magnetic, and Photometric Testing. 

7. Pyrometer Testing and Heat Measurements. 

8 . Testing of Thermometers. 

9. Testing of Glass Volumetric Apparatus. 

10. Legal Weights (in pounds) per Bushel of Various Commodities. 

11. The Standardization of Bomb Calorimeters. 

13. Standard Specifications for Incandescent Electric Lamps. 

14. Samples of Analyzed Irons and Steels—Methods of Analysis. 

15. The International Unit of Light. 

16. The Testing of Hydrometers. 

17. Magnetic Testing. 

18. Standard Gage for Sheet and Plate Iron and Steel. 

19. Standard Density and Volumetric Tables. 

20. Electrical Measuring Instruments. 

21. Precision Measurements of Resistance and Electromotive Force. 

22. Standard Specifications for Transformers, Oil-immersed, Self-cooled, 60-cycle, 2200 Volts. 

23. Standardization of Electrical Practice in Mines. 

24. Publications of the Bureau of Standards. 

25. Standard Analyzed Samples—General Information. 

26. Analyzed Iron and Manganese Ores—Methods of Analysis. 

27. The Testing and Properties of Optical Instruments. 

28. The Determination of the Optical Properties of Materials. 

29. Announcement of a Change in the Value of the International Volt. 

30. Lime: Its Properties and Uses. 

31. Copper Wire Tables. 

32. Standards for Gas Service. 

33. United States Government Specification for Portland Cement. 

34. The Relation of the Horsepower to the Kilowatt. 

35. Melting Points of Chemical Elements and Other Standard Temperatures. 

36. The Testing and Properties of Electrical Condensers. 

37. Electric Wire and Cable Terminology. 

38. The Testing of Rubber Goods. 

39. Specifications for and Measurement of Standard Sieves. 

40. Sodium Oxalate as a Standard in Volumetric Analysis. 

41. Testing and Properties of Textile Materials. 

42. Metallographic Testing. 

43. The Metric Carat. 

44. Polarimetry. 

45. The Testing of Materials. 

46. The Testing of Barometers. 

47. Units of Weight and Measure; Definitions and Tables of Equivalents. 

48. Standard Methods of Gas Testing. 

49. Safety Rules to be observed in the Operation of Electrical Equipment and Lines. 

50. National Standard Hose Couplings and Fittings for Public Fire Service. 

51. Measurement of Time and Tests of Timepieces. 

52. Regulation of Electrotyping Solutions. 

53. The Composition, Properties, and Testing of Printing Inks. 

54. Proposed National Electrical Safety Code. 

55. Measurements for the Household. 

56. Standards for Electric Service. 

57. United States Standard Tables for Petroleum Oils. 


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DEPARTMENT OF COMMERCE 


Circular 

of THE 

Bureau of Standards 

A i 

S. W. STRATTON, Director 


No. 16 


THE TESTING OF HYDROMETERS 


[4th. Udition] 

Issued February 23, 1916 



WASHINGTON 

GOVERNMENT PRINTING OFFICE 
1916 




















• » 














M 







• D. of D. 

MAR 17 1916 




• 3 )^ 0 ),i 


THE TESTING OF HYDROMETERS 


'•fc 

X 


CONTENTS 

Page 

I. Introduction. 4 

II. Specifications for hydrometers. 4 

1. Classes of hydrometers. ^ 

(а) Density.*. 5 

(б) Specific gravity. 5 

(c) Percentage. 5 

(d) Arbitrary scale. 5 

2. General specifications. 5 

(а) Standard temperature. 5 

(б) Material, construction, etc. 5 

(c) Inscriptions. 7 

( d) Tolerances. 7 

3. Special requirements. 8 

(a) Alcoholometers. 8 

(b) Saccharometers. 8 

(c) Hydrometers for sulphuric acid. 9 

{d) Baum6 hydrometers. 9 

(e) Density and specific gravity hydrometers. 9 

(/) Thermohydrometers.. 9 

III. Manipulation of hydrometers. 9 

1. Observing.. ... 10 

2. Influence of temperature. 10 

3. Influence of surface tension.! n 

4. Cleanliness. 13 

IV. Tests performed by the bureau. 13 

1. Instruments admitted for test. 13 

2. Character of test. 14 

(a) Regular test and stamp. 14 

(b) Regular certification. 14 

(c) Special certification. 14 

3. Control marks. 15 

V. Directions for submitting apparatus for tests. 15 

VI. Fees for testing hydrometers. 16 

24546°—16 


3 



































4 


Circular of the Bureau of Standards 

I. INTRODUCTION 


The object of this circular is to present to manufacturers and others the 
information necessary to make possible the construction and verification 
of hydrometers on a uniform basis, to indicate the facilities now available at 
the Bureau of Standards for their verification, and to anticipate the adop¬ 
tion by the Bureau of more comprehensive specification for hydrometers. 

These specifications define the requisite qualifications for hydrometers 
in order that they may be accepted for official verification or test, and are 
provisional in that they are subject to such revision as may render them 
better adapted to the requirements of hydrometer users or to the facilities 
of the makers and of the testing laboratory. 

There are in present use hydrometers for many different purposes, and 
moreover for the same purpose there are in use various hydrometer scales, 
some imperfectly defined, but retained to avoid changes in established 
practice. In considering hydrometer scales the testing of which shall be 
undertaken the Bureau has largely been guided by the present practice. In 
the selection of the scales for definition as standards, suitability to secure 
uniformity and easy realization of such definitions has also been considered. 

In cases where the standard scales chosen differ from those frequently 
used with respect to the standard temperature selected, temperature cor¬ 
rection tables, and, where possible, conversion tables to permit intercom¬ 
parisons between the standard scales and other scales, have been prepared. 
These tables are published in Circular No. 19. 

As in the preparation of specifications for glass volumetric apparatus, 
the regulations 1 of the Kaiserliche Normal-Eichungs-Kommission have been 
freely drawn upon. 

II. SPECIFICATIONS FOR HYDROMETERS 

Two types of hydrometers are comprised in these specifications, namely, 
hydrometers proper, and hydrometers which are combined with thermometers, 
called thermo-hydrometers. 

1 Mitteilungen Der Kaiserlichen Normal-Eichungs-Kommission. Series 2, No. 22; Mar. 9, 
1907. Article 6, Regulations for Hydrometers. 



The Testing of Hydrometers 


5 


1 . CLASSES OF HYDROMETERS 

With reference to indication the following classes of hydrometers are 
included: 

(a) Density Hydrometers, indicating density of a specified liquid, at a 
specified temperature, in specified units. 

(b) Specific Gravity Hydrometers, indicating the specific gravity or 
relative density of a specified liquid, at a specified temperature, in terms 
of water at a specified temperature as unity. 

(c) Per Cent Hydrometers, indicating, at a specified temperature, the 
percentage of a substance in a mixture or solution with water (saccharome- 
ters, alcoholometers, etc.). 

(d ) Arbitrary Scale Hydrometers, indicating concentration or strength 
of a specified liquid referred to an arbitrarily defined scale at a specified 
temperature (Baume hydrometers, etc.). 

2 . GENERAL SPECIFICATIONS 

(a) Standard Temperature.—The specified temperature for use of 
hydrometers or the standard temperature should be 20° C, except as indi¬ 
cated under special requirements. 

( b ) Material, Construction, etc.—Hydrometers should be made of 
Smooth, transparent glass without bubbles, striae, or other imperfections. 
White-black capillary tubes should not be used in thermo-hydrometers. 

The glass should be of a kind which adequately resists the action of 
chemical reagents and also possesses suitable thermal qualities, such as 
would adapt it to use for thermometers. 

The section perpendicular to the axis should be everywhere circular, 
except as elsewhere provided. The stems should be uniform in cross section 
and no irregularities should be perceptible. The outer surface must be 
symmetrical about a vertical axis. There should be no unnecessary thick¬ 
ening of the glass walls, and no abrupt constrictions which would hinder 
convenient cleaning. The capillary stem of a thermo-hydrometer should 
be parallel to the axis and should extend at least io mm above the scale. 
It should contain an enlargement which will permit heating to 120° C. 

Before graduation and adjustment all hydrometers should be thor¬ 
oughly annealed. 

Material used for ballast should be confined to the bottom of the instru¬ 
ment, and no loose material of any sort should be inside a hydrometer. The 
disposition of the weight should be such that the hydrometer will always 
float with its axis vertical. Shot is permitted only in hydrometers without 


6 


Circular of the Bureau of Standards 


thermometers and should be contained in a bulb of suitable size. Bulbs 
containing shot may be flattened, but in all cases the shot must be confined 
in the bottom either by a partition or a cement which does not soften at 
usual temperatures. 

Only mercury is permitted for ballast in thermo-hydrometers except 
those having one bulb, in which the final adjustment may be made by 
securely attaching small strips of paper or other suitable material inside 
the scale. 

Only the best quality of paper should be used for scales and designating 
labels. The paper usually known as first-class ledger paper is suitable for 
this purpose. The scales and labels should be securely fastened in place by 
some material which does not soften at the highest temperature to which the 
instrument will be exposed in use and which does not deteriorate with time. 

The scale should be straight and without twist. 

The instrument should be perfectly dry on the inside when sealed. 
Thermometer bulbs and capillary tubes should be free from air. 

The hydrometer stem should extend above the top of the scale at least 
2 cm and below the scale must continue cylindrical for at least 3 mm. 
The thermometer scale should not extend beyond the cylindrical portion of 
the containing tube nor beyond the straight portion of the capillary. If 
within the stem, it must be above the hydrometer scale. 

It is desirable that the thermometer scale should include the ice point 

(o° C). 

The total length of any hydrometer should not exceed 45 cm and should 
generally be much less than this for the sake of convenience. 

The top of the stem should be neatly rounded, but not unnecessarily 
thickened. 

The graduation and inscriptions should be in permanent black ink, 
such as india ink. They should be clear and distinct. 

The length of the smallest subdivisions of the scales should not, in 
general, be less than 1 mm. In certain cases the subdivisions on the hydrom¬ 
eter scale may be less, but never less than 0.5 mm. The smallest subdi¬ 
visions should never exceed 2 mm in length. 

The division lines must be perpendicular to the axis of the hydrometer; 
that is, horizontal when the instrument is floating. 

The lengths of division and subdivision lines both on hydrometer and 
thermometer scales should be so chosen as to facilitate readings. Sufficient 
lines should be numbered to clearly indicate the reading at any point. The 
numbers at the ends of the scale intervals should be complete, but those 
intermediate may be abbreviated. 


The Testing of Hydrometers 


7 


The division lines of the hydrometer scale should extend at least one- 
fourth around the circumference of the stem and be adjacent to or intersect 
a line parallel to the axis indicating the front of the scale. The division 
lines of the thermometer scale should extend behind and on both sides of 
the capillary. 

To facilitate readings near the end of the hydrometer scale the gradua¬ 
tions should be continued a few divisions beyond the ends of the principal 
interval. 

The hydrometer scale for density indications should be divided in o.ooi, 
0.0005, 0.0002, or 0.0001 units of the density. For per cent or degree indi¬ 
cations the hydrometer scale should be divided into whole, half, fifth, or 
tenth per cents or degrees (never to fourths). 

The thermometer scale should be divided into whole or half degrees. 

No hydrometer should have more than one hydrometer scale or more 
than one thermometer scale, and no secondary or auxiliary graduations 
should be on either. 

(c) Inscriptions.—The hydrometer scale or a suitable special label 
should bear an inscription which indicates unequivocally the purpose of the 
instrument. This inscription should denote the liquid for which the instru¬ 
ment is intended, the temperature at which it is to be used, and the char¬ 
acter of the indication, including definition of any arbitrary scale employed. 

The maker’s name or trade-mark, date of manufacture, and an identifi¬ 
cation number should be inscribed upon the hydrometer scale or label. 

The designation of standard temperature and reference temperature 

I s° 

may be abbreviated, as, for example, Sp. Gr. ^C, meaning that the hydrom¬ 
eter indicates at 15 0 C the specific gravity of the liquid referred to water 
at 15 0 C as unity. 

( d ) Tolerances.—The greatest error of the hydrometer scale should 


not exceed the following: 

Smallest subdivision of hydrometer scale 

Limit of error 

Whole or half per cents or degrees. 

One-half smallest division 

One smallest division 

Fifth or tenth per cents or degrees or any 
density subdivision 








8 


Circular of the Bureau of Standards 


f 

The greatest error of thermometer scales in thermohydrometers should 


not exceed the following: 

Smallest division of thermometer scale 

Limit of error 

1?0 C 

0?4 C 

0?5 C 

0?25 C 


There should be no apparent irregularities in either the hydrometer 
scale or the thermometer scale. 


3. SPECIAL REQUIREMENTS 

The tables chosen for use as basis for standardization of hydrometers 
by this Bureau are contained in Bureau Circular No. 19 (5th ed.), and are 
referred to below by numbers used in that circular. 

(а) Alcoholometers.— Alcoholometers may be graduated to indicate 
the percentage of ethyl alcohol, either by weight or by volume, in mixtures 
of ethyl alcohol and water, or they may be graduated to indicate percentages 
of “proof spirit” as defined by the Bureau of Internal Revenue, United 
States Treasury Department. 

The basis for the graduation of hydrometers to indicate percentage of 
alcohol by weight at 20° C should be Table 2, Circular No. 19. 

The basis for the graduation of hydrometers to indicate percentage of 
alcohol by volume at 6o° F or percentage of proof spirit at 6o° F should be 
Table 3, Circular No. 19. 

Master scales for the graduation of hydrometers to indicate percentage 
of alcohol by weight and by volume and percentage of proof spirit are* given 
in Tables 48 and 49, Circular No. 19. 

Upon alcoholometers subdivided into fifths or tenths of per cent the 
length of the smallest scale intervals may be as small as 0.8 mm. 

(б) Saccharometers. —Saccharometers should be graduated to indicate 
percentage of suger according to weight. 

The basis for graduation of saccharometers, standard at 20° C, should 
be density at 20° C, Table 12, Circular No. 19. 

Brix saccharometers should be graduated to indicate the percentage of 
sugar by weight at 17?5 C and Balling saccharometers the percentage of 
sugar by weight at 6o° F. 

The smallest scale interval of saccharometers may be the same as for 
alcoholometers. 

(c) Hydrometers for Sulphuric Acid. —The basis for the graduation of 
hydrometers indicating per cent of sulphuric acid by weight in mixtures of 
acid with water should be density at 20° C, Table 13, Circular No. 19. 






The Testing of Hydrometers 


9 


(d) Baume Hydrometers.—The basis for hydrometers indicating 
degrees Baume of liquids lighter than water should be the relation to specific 

gravity at ^6 FC^ given by the formula: 

140 


Degrees Baume - 


■ 130 Table 21, Circular No. 19. 


"Sp. Gr. U F 

For hydrometers indicating degrees Baume of liquids heavier than 
water, the basis should be the relation to specific gravity at ^5 T C ^ 

given by the formula: 

Degrees Baume = 145— Table 19, Circular No. 19. 

The liquids for standardization of Baume hydrometers should be in 
general mineral oils for light liquids, and mixtures of sulphuric acid and 
water for heavier liquids. 

(e) Density and Specific Gravity Hydrometers.—Hydrometers indi¬ 
cating density and specific gravity should be graduated to indicate at a 
standard temperature the density, in grams per milliliter or the specific 
gravity in terms of water, at a specified temperature of one only of the 
following liquids within the given range: 


Liquids 

Range 

Liquids 

Range 

Mineral oil. 

0.62-1.00 

Caustic soda. 

1.00-1.55 

Sulphuric acid . 

1.00-1.85 

Common salt. 

1.00-1.23 

Nitric acid . 

1.00-1.55 

Ammonia. 

0.85-1.00 

Hydrochloric acid. 

1.00-1.25 



(/) Thermohydrometers.—Hydrometers containing thermometers should 
not contain temperature “correction tables,” as such tables can, in general, 
be correct for only a very limited portion of the hydrometer scale. Accu¬ 
rate correction tables for the more common liquids (sugar, sulphuric acid, 
ethyl alcohol, and mineral oils) are given in Circulars 19 and 57. 

III. MANIPULATION OF HYDROMETERS 

Hydrometers are seldom used for the greatest accuracy, as the usual 
conditions under which they are used preclude such special manipulation 
and exact observation as are necessary to obtain high precision. It is, 
nevertheless, important that they be accurately graduated to avoid, as far 
as possible, the use of instrumental corrections, and to obtain this result it 




















io Circular of the Bureau of Standards 

is necessary to employ certain precautions and methods in standardizing 
these instruments. 

The methods of manipulation described below are, in general, the ones 
employed at this Bureau in testing hydrometers and should be followed by 
the maker or user to a degree depending on the accuracy required. 

1. OBSERVING 

The hydrometer should be clean, dry, and at the temperature of the 
liquid before immersing to make a reading. 

The liquid in which the observation is made should be contained in a 
clear, smooth glass vessel of suitable size and shape. 

By means of the stirrer which reaches to the bottom of the vessel, the 
liquid should be thoroughly mixed. 

The hydrometer is slowly immersed in the liquid slightly beyond the 
point where it floats naturally and then allowed to float freely. 

The scale reading should not be made until the liquid and hydrometer 
are free from air bubbles and at rest. 

In reading the hydrometer scale the eye is placed slightly below the 
plane of the surface of the test liquid; it is raised slowly until the surface, 
seen as an ellipse, becomes a straight line. The point where this line cuts 
the hydrometer scale should be taken as the reading of the hydrometer. 

In reading the thermometer scale, errors of parallax are avoided by so 
placing the eye that near the end of the mercury column the portions on 
either side of the stem and that seen through the capillary appear to lie in 
a straight line. The line of sight is then normal to the stem. 

2. INFLUENCE OF TEMPERATURE 

In order that a hydrometer may correctly indicate the density or 
strength of a specified liquid, it is essential that the liquid be uniform 
throughout and at the standard temperature. 

To insure uniformity in the liquid, stirring is required shortly before 
making the observation. This stirring should be complete and may be 
well accomplished by a perforated disk or spiral at the end of a rod long 
enough to reach the bottom of the vessel. Motion of this stirrer from top 
to bottom serves to disperse layers of the liquid of different density. 

The liquid should be at nearly the temperature of the surrounding 
atmosphere, as otherwise its temperature will be changing during the 
observation, causing not only differences in density but also doubt as to 
the actual temperature. When the temperature at which the hydrometer 









































































I 

















i 


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t 













I 


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f 


















































I 





Fig. 1.— Section of hydrometer comparator Fig. 2 —Hydrometer comparator 

A is the cylinder containing the test liquid. B is a glass tube for filling and emptying A. C is a siphon for removing the liquid from D into A. 
E is a propeller which stirs the liquid and raises it in the tube F making it flow through G into A and through the cross tube H into D. 
I is a hydrometer. K is a thermometer. 























































































































The Testing of Hydrometers 


ii 


is observed differs from the standard temperature of the instrument, the 
reading is not truly the density according to the basis of the instrument 
or the quality of the liquid according to per cent or arbitrary scale, but a 
figure which differs from the normal reading by an amount depending on 
the difference in temperature and on the relative thermal expansions of the 
instrument and the particular liquid. 

If the latter properties are known, tables of corrections for temperature 
may be prepared for use with hydrometers at various temperatures. Such 
tables should be used with caution, and only for approximate results when 
the temperature differs much from the standard temperature or from the 
temperature of the surrounding air. 

3. INFLUENCE OF SURFACE TENSION 

Surface tension effects on hydrometer observations are a consequence 
of the downward force exerted on the stem by the curved surface or meniscus, 
which rises about the stem, and affects the depth of immersion and conse¬ 
quent scale reading. 

Because a hydrometer will indicate differently in two liquids having 
the same density but different surface tensions, and since surface tension is a 
specific property of liquids, it is necessary to specify the liquid for which 
a hydrometer is intended. 

Although hydrometers of equivalent dimensions may be compared, 
without error, in a liquid differing in surface tension from the specified 
liquid, comparisons of dissimilar instruments in suck a liquid must be 
corrected for the effect of the surface tension. 

In many liquids spontaneous changes in surface tension occur due to 
the formation of surface films of impurities, which may come from the 
apparatus, the liquid, or the air. 

Errors from this cause are avoided either by the use of liquids not 
subject to such changes, which, however, require correction of the results 
by calculation, or by the purification of the surface by overflowing imme¬ 
diately before making the observation. This latter method is employed 
at this Bureau for testing hydrometers in sulphuric-acid solutions and 
alcohol solutions, and is accomplished by causing the liquid to overflow 
from the part of the apparatus in which the hydrometer is immersed by a 
small rapidly rotating propeller which serves also to stir the liquid. The 
apparatus is shown in Figs, i and 2. 


12 


Circular of the Bureau of Standards 


A more simple apparatus 
for hydrometer use, designed 
to permit renewal of the sur¬ 
face by overflowing, is shown 
in Fig. 3. 

The manipulation is as fol¬ 
lows: The cylinder is filled 
nearly to the spout by the 
liquid whose density is de¬ 
sired or in which hydrom¬ 
eters are to be compared. 
The hydrometer is then im¬ 
mersed in the liquid and per¬ 
mitted to float freely until 
it has assumed the tem¬ 
perature of the liquid. The 
hydrometer is raised to per¬ 
mit thorough stirring of the 
liquid. The temperature is 
observed if desired. From 
a beaker of the same liquid 
enough is poured into the 
funnel to cause the liquid to 
overflow and run out the 
spout, where it is caught in 
a convenient vessel. 

The hydrometer is then 
read. The completeness of 
the cleansing of the surface 
of the liquid may be tested 
by repeating the operation, 
as the readings will approach 
a constant value as the sur¬ 
face becomes normal. 

The necessity for such 

Fig. 3 .-Special hydrometer cylinder in use spedal manipu l ation is con . 

fined to the reading of hydrometers in liquids which are subject to surface 
contamination. Such, in general, are aqueous solutions or mixtures of 


















The Testing of Hydrometers 


13 


acids, alkalies, salts, sugar, and weak alcoholic mixtures. Oils, alcoholic 
mixtures of strength above 40 per cent by volume, and other liquids of 
relatively low surface tension are not, in general, liable to surface con¬ 
tamination sufficient to cause appreciable changes in hydrometer readings. 

4. CLEANLINESS 

The accuracy of hydrometer observations depends, in many cases, upon 
the cleanliness of the instruments and of the liquids in which the observations 
are made. 

In order that readings shall be uniform and reproducible, the surface 
of the hydrometers, and especially of the stem, must be clean, so that the 
liquid will rise uniformly and merge into an imperceptible film on the stem. 

The readiness with which this condition is fulfilled depends somewhat 
upon the character of the liquid, certain liquids, such as mineral oils and 
strong alcoholic mixtures, adhere to the stem very readily, while with weak 
aqueous solutions of sugar, salts, acids, and alcohol, scrupulous cleaning 
of the stem is required in order to secure the normal condition. 

Before being tested, hydrometers are thoroughly washed in soap and 
water, rinsed, and dried by wiping with a clean linen cloth. 

If to be used in aqueous solutions which do not adhere readily, the 
stems are dipped into strong alcohol and immediately wiped dry with a 
soft, clean, linen cloth. 

IV. TESTS PERFORMED BY THE BUREAU 
1. INSTRUMENTS ADMITTED FOR TEST 

At present the Bureau is prepared to test hydrometers and thermo¬ 
hydrometers of the kinds indicated below, which conform to the specifica¬ 
tions of this circular: 

Alcoholometers. 

Saccharometers. 

Baume hydrometers for mineral oils or for sulphuric acid. 

Hydrometers indicating density or specific gravity of mineral oils or of 
sulphuric acid. 

Hydrometers indicating per cent of sulphuric* acid. 

Instruments in addition to the above are later to be included in those 
regularly admitted for test, but until further notice instruments other than 
the above should not be submitted for test without previous arrangement 
being made. 


14 


Circular of the Bureau of Standards 


2. CHARACTER OF TEST 

Three kinds of tests are made: (a) Regular test for precision stamp 
without certificate, (6) certification of corrections with precision stamp, 
and (c) special certification of corrections without precision stamp. 

(a) The Regular Test (viz, preliminary examination, verification of 
the hydrometer scale, and of the thermometer scale when this is included) 
determines whether the instrument is qualified to receive the precision 
stamp indicating an approved degree of accuracy. This test (usually per¬ 
formed in the order given above) is continued far enough to indicate with 
reasonable certainty whether the instrument complies with the specifica¬ 
tions. Upon instruments which pass this test the precision stamp, described 
below, is etched. Hydrometers submitted with request simply to “test,” 
or with instructions not otherwise sufficiently explicit, are tested in this 
manner. A fee is charged as given under schedule 28, (a) or ( b ), depending 
upon whether one or both scales are actually tested. 

If the result of examination and test of any hydrometer or thermo¬ 
hydrometer indicates a satisfactory conformity to the specifications, the 
official precision stamp, consisting of the letters “U. S.” and the year 
date, is etched as shown below: 


(b) Regular Certification of corrections with precision stamp. A 
hydrometer qualified to receive the precision stamp as described above, if 
request is made when test is submitted, will be assigned a certification number 
in addition to the precision stamp, and a certificate of corrections will be 
furnished. If certificate is desired only in case the instrument receives the 
precision stamp, the request for test should instruct to “certify and stamp.” 
Three points will be certified unless more are requested. A fee is charged 
as given in schedule 28. 

(c) Special Certification of corrections without precision stamp. A 
hydrometer not qualified to receive the precision stamp because of non¬ 
conformity with the specifications either as to construction or errors tolerated 
will, if found suited to the testing facilities of this Bureau and adapted to 
the intended purpose, be tested as a special instrument and given a certifica¬ 
tion number and certificate as described under (a). If certificate is desired 
regardless of whether the instrument receives the precision stamp the 
request for test should instruct to “ certify specially” If not thus specifically 



The Testing of Hydrometers 


15 


requested, hydrometers will be certified only if they comply with the specifi¬ 
cations, but hydrometers submitted for special certification, if found quali¬ 
fied, will always receive the precision stamp. Special tests are made only 
at the discretion of the Bureau. A fee is charged according to schedule 28. 

Upon instruments for which corrections are certified a certification 
number is etched as shown below: 

B S No. 256 
1916 

3. CONTROL MARKS 

In addition to the certification number on certified hydrometers and 
other hydrometers tested and stamped, the weight in milligrams of the 
instrument against brass weights in air at 760 mm pressure and 20° C will 
be stamped if the sender so requests. 

V. DIRECTIONS FOR SUBMITTING APPARATUS FOR TEST 

Application for Test.—The request for test should be made in writing 
and should include a complete list of the apparatus and a statement of the 
nature of the test desired as explained under IV, 2. 

The sender should always examine apparatus carefully before sub¬ 
mitting it for test, to ascertain if it complies with specifications, thus avoiding 
the loss of transportation on apparatus not qualified for the test desired. 

Purchasers of apparatus to be submitted to the Bureau for test should 
give the dealer advance notice in order to avoid unnecessary delays and 
mis understandings. 

Identification Marks.—Instruments and the packages in which they 
are shipped should both be plainly marked to facilitate identification, pref¬ 
erably with the name of the manufacturer or shipper, and a special reference 
number should be given to each article, which should be referred to in the 
correspondence concerning the test. After receipt at the Bureau the B. S. 
test number should also be used. 

Shipping Directions.—Instruments should be securely packed in cases 
or packages, which may be used in returning them to the owner. In all cases 
transportation charges are payable by the party desiring the test and should 
be prepaid. Apparatus must be accompanied by an itemized shipping 
invoice. 

Breakage.—No risk of breakage will be assumed by the Bureau. All 
possible care will be taken in handling the apparatus submitted for test, 


i6 


Circular of the Bureau of Standards 


but a certain amount of breakage is unavoidable and must be borne by the 
owner. 

Address. —Articles should be addressed, “Bureau of Standards, Wash¬ 
ington, D. C. delays incident to other forms of addresses will thus be 
avoided. Articles delivered in person or by messenger should be left at 
the shipping office of the Bureau, and should be accompanied by a written 
request for the verification. 

Remittances. —Fees should be remitted by money order drawn to the 
order of the “Bureau of Standards,’’ and should be sent with the request 
for test whenever practicable. Delays in forwarding fees involve corre¬ 
sponding delays in the return of articles tested, as the articles are held 
until the fees due thereon have been paid. 

All communications should be addressed, “ Bureau of Standards, 
Washington, D. C.” 

VI. FEES FOR TESTING HYDROMETERS 


SCHEDULE 28.—HYDROMETERS AND THERMO-HYDROMETERS 


(a) Test of hydrometer to determine whether it complies with Bureau requirements for 


precision stamp. $i. oo 

(&) Test of thermo-hydrometer, as under (a), including test of thermometer scale. i. 75 

(c) Certificate of corrections at three points on either or both scales, additional fee.50 

( d ) For additional points certified, each extra point.25 

(e) For determination of weight of instrument, additional fee.25 

(/) For supplying missing identificaiion numbers, charges for each number.20 


(g) For special tests not enumerated above, reasonable fees will be charged depending upon the 
nature of the test. 


Approved: 

William C. Redfield, 

Secretary. 


S. W. Stratton, 

Director. 












/ 

























Gaylord Bros. 
Makers 

Syracuse, N. Y 
PAT. JAN. 21, 1905 




















































